feat!: upgrade to eslint 9, update configs

BREAKING CHANGE: this changes the configuration format,
also adds support for module, and commonjs types

packages/eslint-config/scripts/postinstall.cjs

@@ -0,0 +1,34 @@
+'use strict'
+
+const fs = require('fs')
+const path = require('path')
+// noinspection NpmUsedModulesInstalled
+const process = require('process')
+const checkConfig = require('@ivuorinen/config-checker')
+const foundConfig = checkConfig('eslint')
+
+if (foundConfig.length > 0) {
+  console.log('eslint-config: Found existing eslint config file, skipping creation.')
+  console.log('eslint-config: If you want to create a new config file, please remove the existing one.')
+  console.log(`eslint-config: Found config files at: ${foundConfig.join(', ')}`)
+  process.exit(0)
+}
+
+const filePath = path.join(process.env.INIT_CWD, 'eslint.config.mjs')
+const fileConfig = `import ivuorinenConfig from '@ivuorinen/eslint-config';
+
+export default [
+  ...ivuorinenConfig,
+
+  // your modifications
+  {
+    rules: {
+      // "no-unused-vars": "warn"
+    }
+  }
+];
+`
+
+if (!fs.existsSync(filePath)) {
+  fs.writeFileSync(filePath, fileConfig)
+}